Lust isn't a sin; it's an emotional manifestation of biochemical stimulae. The behavior that stems from it may be sinful (or at least bad), but it certainly doesn't have to be; that is an entirely different issue. And lack of \"responsible lust\" in a marriage is indeed a potential problem.

my wife WANTS that I lust about her ... and most of the time, she is very pleased when I make (censored) remarks about her beautiful body and approach her in (censored) ways. Except when she has PMS ... then I know that I should keep away from her, because of self-protection ...